Aerospace sealants are widely used in aircraft production as both fuel tank and fuselage sealing systems. Brushcoat (Class A) sealants and fillet (Class B) sealants may be used as a B over A system or B-only system. For composite fuel tanks, in particular, the dimensional application requirements are very stringent, for example, to ensure integrity where the sealant system is used as an ignition source prevention feature during a lightning strike event. When these requirements are not met, sealant must be removed and the area reworked. The allowed methods for sealant removal are carefully controlled to avoid damage to the underlying composite, limiting the technicians to tedious and time-consuming tools and processes, such as scraping with plastic tools.
Aerospace sealants are very difficult to remove from composite or metal substrates by traditional mechanical or chemical means. There are very few chemicals available that sufficiently weaken the sealant to aid in removal and even fewer that do not introduce a risk to an underlying composite substrate. Mechanical means are typically limited to scrapers. When the underlying substrate is a composite, these scrapers are made of a material softer than the composite to avoid damage. Use of either, or both, mechanical means and chemical means may be a slow process, potentially taking hours to complete.
The existing solutions for aircraft applications include (a) mechanical means by using manual or automated scrapers made of materials softer than the substrate and (b) chemical means by using extremely basic or acidic materials to soften the sealant. Method (a) is a very delicate and lengthy process to avoid damaging the substrates, especially composite substrates. Method (b) is a very delicate and often lengthy process as the chemicals can easily damage coated and uncoated substrates. For metal substrates, the risk is the potential for initiation of corrosion. For composites, the risk is structural degradation of the substrate through gouging and damage to the underlying load bearing composite material.
Hence, there is a need for sealant removal methods, systems, and devices that are less delicate, less likely to damage the substrate, less time consuming, and/or less tedious.